Known types of computer/communications network monitors are available to provide on-line analysis of bit-error-rates (BERs). Also, protocol analyzers are available for Wide Areas Networks (WANs) and Local Area Networks (LANs) that provide simulated network components, perform BER tests, and perform link level performance analysis. However, these conventional types of monitors and analyzers work only with known communications protocols.
Examples of conventional systems include the following. In U.S. Pat. No. 4,920,537 there is described a method for in-service measurement of the BER of a data stream in a digital communications circuit. This method is said to allow bit error rates to be measured without the need to insert a known test signal onto the communications channel. This is accomplished through the use of two, synchronized test sets to recover and compare block-check codes.
In U.S. Pat. No. 4,916,694 there is described a method for measuring the statistics of traffic loading on a packet network without actually decoding the data. This is accomplished by detecting the presence of a signal carrier on a packet network, and recording the time of the detected event. This approach assumes the presence of an ON/OFF carrier where the carrier in ON only when a packet is being sent. That is, this patent does not consider the case of a synchronous circuits where there is a continuous carrier. The method described by this patent does not attempt to identify the protocol or its characteristics.
In U.S. Pat. No. 4,792,753 there is described a system for accomplishing an automatic, real-time analysis of traffic loading on a local area network by recovering individual packets, and measuring a time between packets and packet length. However, this approach requires specific, a priori knowledge of the packet structure.
What is not provided by known types of network and protocol analyzers, and what is thus a first object of the invention to provide, is a method and apparatus to recover data format and network protocol information from a data stream for a case where the specific protocols on the network under examination are unknown, and in fact, may never have been previously encountered by an operator analyst.
A further object of the invention is to provide a method and apparatus whereby an operator analyst is enabled to detect and observe various elements that are common to many time-division-multiplex (TDM) and packet protocol formats.